摘要：Given a collection of distinct numbers, return all possible permutations. For example,[1,2,3] have the following permutations: 这题是列举所有情况，回溯。 每次都是从头开始遍 阅读全文

摘要：Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers. If such arrangement is not possib 阅读全文

摘要：Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand. (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2). You a 阅读全文

摘要：Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules. The Sudoku board could be partially filled, where empty cells are filled wit 阅读全文

摘要：Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T. Each num 阅读全文

摘要：Given a set of candidate numbers (C) (without duplicates) and a target number (T), find all unique combinations in C where the candidate numbers sums 阅读全文

摘要：Given a linked list, swap every two adjacent nodes and return its head. For example,Given 1->2->3->4, you should return the list as 2->1->4->3. Your a 阅读全文

摘要：Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array whic 阅读全文

摘要：Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. 阅读全文

摘要：Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of 阅读全文

摘要：Input is guaranteed to be within the range from 1 to 3999. 将整数转成罗马数字。。下面答案比较厉害了。它将每个位置上（每位数）可能出现的情况先列出来，然后匹配 阅读全文

摘要：将字符串转成整数，跳过前面的空格。。然后转的时候注意防止溢出。。total=total*10+digit 这个检查溢出的方式要掌握：最大整数除以10比total小（说明total*10就要溢出），当最大整数除以10等于total，且余数小于digit，那么执行上面公式也会溢出。。 if(Intege 阅读全文

摘要：The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font 阅读全文

摘要：Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000. Example: Example: 从字符串中找出最长的回文子串，该 阅读全文

摘要：Given a string, find the length of the longest substring without repeating characters. Examples: Given "abcabcbb", the answer is "abc", which the leng 阅读全文

摘要：Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telepho 阅读全文

摘要：Given a linked list, remove the nth node from the end of list and return its head. For example, Given linked list: 1->2->3->4->5, and n = 2. After rem 阅读全文

摘要：Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n = 3, a solution set is: 给 阅读全文

摘要：You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contai 阅读全文

摘要：Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times. You may assume that the 阅读全文